Don't get the portable ones. I made the mistake in 2019 and the thing is abysmally loud, barely gets the temperature 2 degrees lower in a single room, uses twice as much electricity as the rest of the household combined, and you still can't work from the heat and noise. That's with a window replaced by an insulating panel with a round cut-out for the hose, not a cracked window like you see most people needing to do. I've compared about two dozen units in a spreadsheet and this one was clearly the best buy, so I don't think it's just my unit

I totally recommend airco but only the split units that actually provide relief. Still a lot of energy but I feel differently about that consumption when it's not mostly wasted

The mobile ones are nice to aim at you though, I'll give them that much. For the effect they give, you might nearly just as well run it outside (anywhere in the shade) and aim it at you. Then the noise also doesn't reflect off the walls so that's more bearable, too

Btw the split units, as a bonus, can usually also heat the room(s) they're in. The UK has quite a lot of (planned) wind power year round, so reducing gas consumption will also cut back on the fuels that are causing this